Ensure End of Line conversion does not happen on windows

Running git clone http://github.com/dimagi/commcarehq-venv in windows causes the end of line characters to be converted from the linux standard (lf) to windows standard (crlf). This causes errors when running source /home/travis/virtualenv/bin/activate in Vagrant because windows has inserted a $/r at the end of each line break. This change ensures that all text files retain the linux standard (lf) end of line character. 

Reference:
https://help.github.com/articles/dealing-with-line-endings
I think there's a typo here. Looks like "download" but I still don't fully follow (comment copied from https://github.com/dimagi/commcarehq-venv/pull/4)